The visible part of the electromagnetic spectrum is represented by less than an octave of the keys; UV, IR, and microwaves are also indicated.
What it shows:
The keys of a piano are used to represent the electromagnetic spectrum, illustrating the narrow range of frequencies that constitute the portion visible to human sight.
How it works:
An old piano 1 with its center octave of keys (C4=261.6Hz to C5=523.3Hz) colored for the visible spectrum (the seven colors spread to include eight keys). The visible spectrum covers just under 1 octave: violet at 7.5×1014Hz to red at 4.0×1014Hz, whereas human hearing ranges about eleven octaves (20Hz to 20kHz).
The electromagnetic spectrum however covers at least fifty octaves from the radio to gamma radiation; but with the visible region covering this amount of keyboard, the piano can only play near infra-red to near ultra-violet.
Setting it up:
With the keyboard facing the audience. If the lecturer is no maestro on the ivories a volunteer from the audience will be required.
A clue to the hidden universe becoming visible to us with UV and IR observing technology can be gotten by playing a little tune on the spectrum piano. Choose a popular piece (something instantly recognizable 2 ), but play it first using only the visible spectrum keys (name that tune?). Extend your technology into the IR, then into the UV.
1 Bogart (New York) Grand Upright
2 Beethoven's Für Elise worked tremendously well, performed by student assistant Alyn Kelley '90.